linux-kernel - Re: [PATCH v4] mm: prevent endless growth of anon

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Message-ID: <5491B031.3070107@redhat.com>
Date:	Wed, 17 Dec 2014 11:32:49 -0500
From:	Rik van Riel <riel@...hat.com>
To:	Konstantin Khlebnikov <koct9i@...il.com>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
CC:	Andrea Arcangeli <aarcange@...hat.com>,
	Tim Hartrick <tim@...ecast.com>,
	Daniel Forrest <dan.forrest@...c.wisc.edu>,
	Hugh Dickins <hughd@...gle.com>, Michal Hocko <mhocko@...e.cz>,
	Michel Lespinasse <walken@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH v4] mm: prevent endless growth of anon_vma hierarchy

On 12/17/2014 02:57 AM, Konstantin Khlebnikov wrote:

> @@ -236,6 +240,13 @@ static inline void unlock_anon_vma_root(struct anon_vma *root)
>  /*
>   * Attach the anon_vmas from src to dst.
>   * Returns 0 on success, -ENOMEM on failure.
> + *
> + * If dst->anon_vma is NULL this function tries to find and reuse existing
> + * anon_vma which has no vmas and only one child anon_vma. This prevents
> + * degradation of anon_vma hierarchy to endless linear chain in case of
> + * constantly forking task. In other hand anon_vma with more than one child
> + * isn't reused even if was no alive vma, thus rmap walker has a good chance
> + * to avoid scanning whole hieraryhy when it searches where page is mapped.
                              ^^^^^^^^^
                              hierarchy

Other than that:

Reviewed-by: Rik van Riel <riel@...hat.com>


Thanks for fixing this long standing issue, Konstantin.
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